Natural Hazards HO Pui-sing Contents What are natural hazards Flooding Drought Natural environment Natural environment has provided man with useful resources . Natural environment may be classified into four categories: Physical : energy, mineral and soil resources;
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Blizzard and snow
Avalanche – rock
Bacterial, viral and protozoal disease
Avalanche – snow
Foot and mouth disease
Lightning strike and fire
WindstormClassification of hazards
It is the most important indicator.
Magnitude rate as ‘extreme’ happenings and pose sufficient threats to the human system to be considered natural hazards.
The Richter Scale
Speed of onset
It refers to the length of time between the first appearance or warning of an event and its peak.
Slow-onset hazards(drought and soil erosion)
Rapid-onset hazards(floods and earthquakes)Six Indicators
It refers to the period of time over which it occurs.
Droughts: seasons or years
Floods: days or weeks
Tornados: minutes or hours
It refers to how often an event of a given magnitude may be expected to re-occur.
‘Return period’: a recurrence interval of 10 years is to say it has in any year a 10% chance of occurring.Six Indicators – (cont’d)
The area of natural hazards affect.
Avalanche: short and narrow belt of the landscape.
Drought or flood: several thousand km.
Predictability of an natural hazards occur in an given area.
Predictable and possible for planning.
Volcanic eruptions: fixed point (volcano)
Floods: channels and flood plains
Tropical cyclones: several erratic paths
Earthquakes: unknownSix Indicators – (cont’d)
Bangladesh (1970) vs United States (1969)
Poor farming methods
Cut ditches to improve the drainage of their moorland
Heavy rain storms
Erosion of peat
The land sinking / Sea level rising
No vegetation cover in highland
Poor mining method to enhance the land sinks
Poor management of embankmentsCauses of Floods
Vaiont dam overtopped
Pakistan and India
2.27 million crop ha at loss of $63 million
Huang He, China
3.6 million affected
Chang Jiang, China
Huang he overflowed, communities destroyed
Huang He, China
Kaifeng city was completely destroyedImpacts of floods
2. Crops damaged and loss of livestock
3. Disrupting transport system / network
4. Fertile soil wash away from farmland (soil erosion)
5. Rivers become shallow due to soil deposition (not suitable for navigation)
6. Reduce storage capacity of reservoirsImpacts of Floods – cont’d
What were the impacts of floods on people and the environment?
People like to make a rational choice of responses.
Few people have access to full information
Many are just not aware of all the alternativeresponses available
People differ in their ability
Few like to forget previous painful history
People make choices that help them achieve a satisfactory level of reward, but
Stop short of striving for the highest possible level.
Accept ‘tolerable’ levels of hazard
Avoid the worst of the impact
Their property is insured anyway.People’s perception – cont’d
Access to full information.
Strong networked of family
Strong friendship support
Strong wealth and political powerPeople’s Choices
planners take proper and consistent account of flood hazards.
flood heights as the determinants of action.
alternatives to repetitive rebuilding.
3, 4, 8, 10
3, 4, 8
2, 6, 8
1, 5, 7, 9, 10
1, 5, 7
Relief and Reconstruction